Based on customer feedback I felt it was important to clarify a few key points about PLA and also the advantages and disadvantages of PLA vs ABS when used on FFD printers (such as the Makerbot Replicator, UP!, etc.).
Firstly I'd like to say that PLA is a very strong and very durable material.
There are a few myths surrounding PLA:
Myth 1: PLA will dissolve in water and/or will degrade in moist environments.
This not true.
The plastic that dissolves in water is PVA, not PLA.
Myth 2: Because PLA is biodegradable it will self destruct and just become undone in a matter of months
Again, not true.
"Biodegradable" means the product is strong and performs its function very well but when you throw it in a landfill it will ultimately break down.
This is actually much more environmentally responsible than using ABS which takes over a hundred years to break down. In addition PLA is made from natural resources such as corn starch or sugar cane.
Myth 3: ABS is much stronger than PLA
This is the most recurring one and it's also the most inaccurate: if you compare injection molded parts, ABS parts are indeed stronger than it's PLA counterparts; however we're doing 3D Printing layer by layer, not injection molding and this changes things considerably:
A 3D printed part in PLA is MUCH stronger than a part printed in ABS. This is because PLA has significantly stronger layer bonding than ABS.
About layer bonding: unlike injection molding, FFD printers print layer by layer so layer bonding is what determines the part strength.
If you're familiar with 3D Printing you'll know that the strength of a part changes depending on the direction: if you pull perpendicularly to the Z axis (where layers are deposited), they will detach; if you pull in any other direction the part is much stronger. It behaves a bit like wood.
Because PLA has much stronger layer bonding it's almost as strong in all directions (even when pulled in the Z axis).
ABS on the other hand, will detach layers much faster and much easily than PLA, making 3D printed ABS parts less strong. (they're not weak either; PLA parts are just stronger).
PLA vs ABS in practice:
Rigidity:
PLA is a much more rigid material compared to ABS. If you compare ABS and PLA by applying a progressive force, ABS will start to bend and finally will break; while ABS is bending, PLA on the other hand will hold it's shape (it's very rigid and doesn't flex).
After a certain point it will eventually break before bending. You often need more force to break a PLA part than an ABS one especially if you have a thick part.
Shrinkage factor:
PLA has a much lower shrinkage factor than ABS.
In practice this means it's MUCH easier to use in 3D printers: unlike ABS, PLA deforms significantly less and suffers from very little layer detachment leading to a much higher success rate on prints.
With ABS, even a relatively small part will deform when printing if you don't have a heated bed and/or a heated building environment.
Painting:
Both materials - PLA and ABS - can be painted andpost processed (sanded)
Bio degradability
PLA is a bio degradable material. This means it will resist for very long in indoors use and occasional outdoors use but permanent exposure to the elements will eventually start to degrade it.
It is not suitable, for example, for parts that need to stay outdoors 365 days a year; for these applications ABS is preferable.
From what we've seen over the years we've been selling 3D Printers there are 3 very specific cases where ABS is preferable over PLA:
Case 1: Outdoors use
We've had a customer of ours that purchased a 3D printer to build enclosures for electronics modules that were going to be left outside for several years.
In this case ABS is better: by not being bio degradable ABS ensures that it will retain its properties exposed to the elements outdoors for several years.
Case 2: Parts that need to flex (for fittings for example)
Another customer of ours needed to build supports for DIN rails. The support needed to flex enough to fit into the DIN rail.
We printed the same part in PLA and ABS. PLA, due to its rigidity, wouldn't flex so ABS was the material of choice because of it's flexibility.
One important note here: the part would flex because it had a thin back plate; if you have a thick ABS part it will obviously not bend as they needed.
Case 3: temperature
We've never had a customer with this need but it's worth mentioning: ABS has a higher melting temperature so if you have applications that need to deal with temperatures above 60ºC, than ABS is also preferable over PLA because ABS has higher glass point and melting point.
All in all PLA is not a "one size fits all" but it will meet the needs of 95% of the customers and - from experience - it is so much easier to use and print compared to ABS.
The fact that is has a low shrinkage factor means parts deform significantly less which results in much higher success rates in 3D prints.
You'll find yourself using your 3D printer a lot more and getting a lot more work done. We have several printers in the lab and we use PLA for 99.5% of the parts we produce, even for our 1m tall Humanoid.
For some reason a myth was built around PLA that steers people away from it and leads them to blindly believe that ABS is a better material for 3D printing. This is not the case for all the reasons above.
I hope this posts helps clear this out.
Taking our offer of 3D Printers, the Replicator 2 (for PLA only) is a great machine. It is designed to provide the smoothest print experience possible in the current state of the technology.
That's the printer we use the most in our lab. That and an old wooden Replicator DUAL (with a number of mods from thingiverse to print PLA and ABS much better)
Regards
Pedro.Statistics: Posted by PedroR — Tue Jul 09, 2013 5:27 pm
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